Research in the Wade Lab encompasses molecular inorganic/organometallic chemistry and materials science with a focus on the design and study of new catalytically active molecules and materials. Current projects involve the synthesis of metal-organic frameworks (MOFs) constructed from catalytically active transition metal complexes, the design of bio-inspired MOF adsorbents for trace CO2 capture, and the investigation of new redox-active ligand platforms. Synthesis plays a central role in our research program, and a variety of solution and solid-state characterization techniques are used to elucidate the structure and properties of newly synthesized materials. These include X-ray diffraction, gas porosimetry, thermogravimetric analysis, ICP-OES, cyclic voltammetry, and NMR, IR, and UV-Vis spectroscopies.
Site-isolation Effects in Metal-Organic Framework Catalysts
Advances in organometallic catalysis have had a profound impact on chemical synthesis in both academic and industrial settings. However, homogeneous organometallic catalysts continue to suffer drawbacks related to stability, product separation, and recyclability. Metal-organic frameworks (MOFs) have emerged as versatile platforms for the design of heterogeneous catalysts that retain many of the beneficial features (e.g. ligand tunability) of homogeneous systems. In addition, catalyst immobilization can improve the lifetime and activity via site-isolation effects. In this project, we are incorporating well-defined organometallic species into MOFs to study the effects of reactive site confinement on small molecule activation processes and catalytic processes such as Lewis acid activation, hydrogenation, and C–H functionalization. We have pioneered the design of “pincerMOFs” assembled from linkers based on transition metal diphosphine pincer complexes. These materials show significant differences in catalytic activity and selectivity compared to homogeneous analogues and have a broad scope of potential applications in catalysis.
Bioinspired MOFs for Trace CO2 Capture
The effect of CO2 on climate change and its potential for use as a renewable chemical feedstock have become strong motivating factors to develop new technologies for CO2 capture and conversion. Technologies that enable efficient capture of CO2 from the atmosphere are highly desirable since they allow remediation and utilization efforts to be distributed away from point sources such as power plants. Current strategies for CO2 removal from air such as aqueous amine scrubbing and causticization with metal hydroxide salts are very energy intensive and may not be economically viable. Solid adsorbents capable of reversibly extracting CO2 from air have the potential to be much more energy efficient and profoundly affect how we address the remediation and utilization of atmospheric CO2. In this project, we are using design strategies inspired by metalloenzymes to develop new MOF adsorbents for CO2 capture under atmospheric conditions. For example, MOFs containing Lewis basic transition metal hydroxide groups show excellent performance for trace CO2 capture via to a CO2/HCO3– chemisorption mechanism and cooperative hydrogen bonding interactions reminiscent of secondary coordination sphere interactions in α-carbonic anhydrase.
New Redox Active Ligand Platforms
Ligand design plays an important role in tuning the activity and selectivity of homogeneous transition metal catalysts. In addition to influencing the electronic properties and steric environment of a metal center, ancillary ligands can play more active roles by aiding in substrate activation via secondary coordination sphere interactions or acting as charge reservoirs. In this project we are designing new ligand platforms that contain redox active arylene diimide (ADI) groups. ADIs are a versatile family of electron deficient molecules that exhibit rich photophysical properties and can reversibly store up to two electrons at mild reducing potentials. We are currently exploring ADI-based ligands that enable photo- and/or electrocatalytic transformations in transition metals complexes by facilitating multi-electron transfer processes and/or acting as Lewis bases to assist in substrate activation.